> One of the things that is going on is that POV-Ray is reasonably
> smart about knowing when it is likely to be helpful to remove
> manual bounding. +UR doesn't remove all manual bounds, only
> manual bounds where POV-Ray thinks it can do better. In this
> case, it has trusted you to provide better manual bounds than it
> would have applied automatically.

Bases on what you say below I assume "better" in this case means
lower volume.  I'd think cross-sectional area relative to the camera
would be a better judge of quality but I'm sure its much easier to
calculate volume.  I think I can follow.  +UR doesn't force the
manual bounds to be removed it just forces this quality check.

> In this case, the automatic bounding box calculated by
> POV-Ray is *considerably* better than the one you provided
> manually.

Volume wise yes but mine shound have had a smaller bounding
slab with the +UD option which I think means that particular
picture would have rendered faster as fewer pixels would have
been checked for ray intersection with that shape.

By the way the reason I didn't use:
    bounded_by { box {<-56, 29, -1>, <56, 141, 1>} }

is I was worred about Co-incident Surface problems.  Note
what happens if you use:
    bounded_by { box {<-56, 29, -1>, <56, 141, 1>} }
    clipped_by {bounded_by}

Should this not be an issue if just the bounded_by statement
is used?

> I would have though that -UR would force it to use the manual
> bounding. However, the documented reason why you would
> want to keep inefficient manual bounds doesn't apply in this
> case, and perhaps POV-Ray is smart enough to have worked
> that out.

So even with the -UR flag you are telling me it does the quality
check and uses what it thinks is better?  So just what is the
difference between -UR and +UR?  Is there one?

> Your manual bounding box has a volume of 50,176 cubic
> units, whereas the automatic bounds calculated by POV-Ray
> has a volume of 28800 cubic units.

I'm guessing 120*120*2.

> A quick experiment shows that POV-Ray is choosing the
> bounds that have the lower volume irrespective of the UR
> setting.

Interesting... sounds like you are coming to the same
conclusion I am.  That being the the UR flag isn't doing
anything.

> Try making the Z values of your manual bounding box a
> closer fit.

Done... and yes it works.  I see the default bounding box has
Co-incident surfaces so I take that to mean I can use them
too.

Thanks,
Carl

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